Air conditioner condensing system control

ABSTRACT

An air conditioner condensing system control having a motor driven means for flowing cooling air in heat transfer association with a condenser thereof. The operation of the motor is controlled by a resistance means in series therewith and disposed in heat transfer association with the air flowed by the air flowing means. The control means further includes means for providing an adjustable additional voltage to the motor for modulating the speed thereof. The additional voltage supply means may comprise an inexpensive gated control element adapted to control only a portion of the total maximum power supply voltage to the motor. Means are provided for sensing the temperature of the condenser at a liquid-gas interface therein for controlling the gated control element.

Elite Ramsey States atent 1 AIR CONDITIONER CONDENSING SYSTEM CONTROL[75] Inventor: Robert W. Ramsey, Nashville, Tenn.

[73] Assignee: Heil-Quaker, Lewisburg, Tenn. [22] Filed: Apr. 12, 1971[21] Appl. No.: 133,276

[451 May 29, 3973 L. Judd and Hofgren, Wegner, Allen, Stellman & Mc-Cord [57] ABSTRACT An air conditioner condensing system control having amotor driven means for flowing cooling air in heat transfer associationwith a condenser thereof. The operation of the motor is controlled by aresistance means in series therewith and disposed in heat transferassociation with the air flowed by the air flowing means. The controlmeans further includes means for providing an adjustable additionalvoltage to the motor for modulating the speed thereof. The additionalvoltage supply means may comprise an inexpensive gated control elementadapted to control only a portion of the total maximum power supplyvoltage to the motor. Means are provided for sensing the tem perature ofthe condenser at a liquid-gas interface therein for controlling thegated control element.

14 Claims, 6 Drawing Figures PATENTED 3. 735.602

F IILIIIIIIIllIIw!|Illlllllllllllllllllllri INVENTOR ROBERT W. RAMSEY #1M, M. M, BY M$m M- ATTORNEYS.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to air conditioning apparatus and in particular to means forcontrolling the operation of a condenser fan in such an air conditioningapparatus.

2. Description of the Prior Art In the conventional air conditioningapparatus utilizing condensers for cooling the compressed refrigerantfluid prior to the delivery thereof to the evaporator, a fan is providedfor cooling the hot compressed refrigerant by heat exchange relationshiptherewith in the condenser. It is desirable to adjust the speed of thefan to vary the cooling effect, such as in accordance with thevariations in temperature of the refrigerant fluid and/or in accordancewith the variations in the ambient temperature conditions. It has beenfound that in conventional refrigeration-systems of this type, aliquid-gas interface level appears in the condenser at a pointintermediate the top and bottom of the condenser during normal operationof the system. It is desirable to vary the cooling effect of the air forregulation of the refrigeration as by varying the speed of the motordriving the air moving means. Conventionally, temperature sensingdevices have been placed in thermal transfer contact with the condenserfor sensing the temperature of the condenser and controlling the speedof the air moving means motor. The known control systems for thispurpose have the serious disadvantage of requiring that the electricalcontrol gated devices used therein handle the full motor current as wellas switch the full supply voltage. Another disadvantage of the knowncontrol devices is the relatively high noise level produced thereby as aresult of the chopped wave characteristics of the electricaloutputprovided for controlling the motor speed. Such chopped wave controlsfurther cause radio frequency interference and disturbances and providesubstantial losses in the operation of the motor.

Another problem found with such conventional control systems is therelative insensitivity of the temperature sensing device resulting fromthe direct thermal contact thereof with the condenser. The provision ofthe sensing element in physical contact with the condenser raises thefurther problem of difficulty of electrical insulation. Still further,it is difficult to preselect the parameters of such a system, therebynecessitating the adjustment of the system for proper operation onlyafter the system is installed in the field. Such field adjustment iscostly and relatively inefficient.

A further disadvantage of the conventional systems is the inabilitythereof to respond directly to variations in ambient air temperatureswhich would effect the required control of the motor speed to producethe desired cooling effect. Still further, the conventional systems arerelatively complicated and expensive. Illustratively, where gatedcontrol devices are utilized for regulating the full load current andsupply voltage of the motor, the cost of the control may be $25.00 ormore.

SUMMARY OF THE INVENTION The present invention comprehends an improvedcontrol for a condenser fan motor eliminating the disadvantages of theabove-discussed prior art devices in a novel and simple manner.

More specifically, the invention comprehends the provision of a motorspeed control system for such use having a voltage reducing resistor inparallel with a gated device for cooperatively delivering desiredoperating voltage to the condenser fan motor. The resistor may be placedin the path of flow of the air moved by the condenser fan so as toprovide improved efficiency in the operation of the system. The gateddevice may comprise a relatively inexpensive electronic gated devicesuch as a silicon controlled rectifier adapted to switch only a portionof the full supply voltage, thereby permitting the use of a relativelyinexpensive device while yet providing accurate modulation of the fanmotor to provide accurate control of the condenser cooling effect.

The invention further comprehends the provision of the temperaturesensing means in spaced relationship to the condenser adjacent the levelof the liquid-gas interface of the refrigerant fluid within thecondenser. Thus, the temperature sensing device is able to respond tovariations in the liquid-gas interface level quickly and accurately toprovide improved control of the fan induced cooling effect. Further, thesensing means may be disposed in thermal transfer association with theairstream drawn by the fan so as to be responsive to the ambienttemperature conditions as well as the refrigerant temperature conditionsin the condenser providing further improved accuracy in the control ofthe cooling effect to maintain the desired head pressure of therefrigerant fluid in the refrigerant system.

The sensing element may be positioned accurately at the factory avoidingthe necessity for adjustment of the system in the field uponinstallation.

Thus, the control of the present invention is extremely simple andeconomical of construction while yet providing highly desirableadvantages over the known condenser fan control devices.

BRIEF DESCRIPTION OF THE DRAWING Other features and advantages of theinvention will be apparent from the following description taken inconnection with the accompanying drawing wherein:

FIG. 1 is a perspective view of a refrigeration unit having a condenserfan control embodying the invention;

FIG. 2 is an enlarged perspective view thereof with the cabinet removed;

FIG. 3 is a top plan view of the apparatus of FIG. 2;

FIG. 4 is an enlarged. top plan view of the resistor and sensing elementmeans of the control with a portion thereof broken away for facilitatedillustration of the arrangement;

FIG. 5 is a fragmentary side elevation taken substantially along theline 5-5 of FIG. 4; and

FIG. 6 is a schematic wiring diagram of the electrical control.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the exemplary embodiment ofthe invention as disclosed in the drawing, a refrigeration unitgenerally designated is shown to comprise a condensing unit of aseparate condenser-evaporator air conditioning system wherein thecondensing unit and compressor are mounted externally of the space to becooled. Illustratively, such a unit may be installed exteriorly of aresidence on a suitable pad (not shown). The condensing unit includes acondenser 11 adapted to be cooled by a suitable air moving means hereincomprising a fan 12 driven by an electric motor 13 for flowing coolantair in heat exchange relationship with the fins 14 of the condenser. Acompressor 15 may be mounted on the base 16 of the apparatus 10 in aseparate space 17 defined by an upright baffle wall 18 at one end of thecondenser. A suitable control 19 may be provided having a capacitor 20for controlling the operation of the motor compressor 15 and the fanmotor 13. A speed control package generally designated 22 includes meansfor adjustably regulating the speed of fan motor 13 in response to thetemperature conditions sensed by a probe 21 carried on baffle wall 18adjacent condenser 11. Speed control package 22 further includes aresistor 23 disposed in the path of flow of the air drawn by fan 12through the condenser. As best seen in FIG. 3, fan 12 is mounted in asuitable shroud 24 for drawing a stream of air inwardly throughcondenser 11 for discharge through outlet grill 25 to the ambientatmosphere. Unit 10 further includes suitable refrigerant lines 27extending between compressor 15 and condenser 11 and suitable electricalwiring harnesses 28 and 29 for electrically interconnecting control 19,control package 22, condenser fan motor 13, motor compressor 15, and thecapacitor 20.

Speed control package 22 includes a circuit board 30 mounted in asuitable housing 31 electrically connected to probe 21 and resistor 23,as shown in FIG. 4. Probe 21 includes at the distal end thereof asensing element, herein a thermistor 32 which, as shown in FIGS. 2 and3, is juxtaposed to the rear face of the condenser adjacent the normalliquid-gas interface 33 of the refrigerant fluid in the system. Asresistor 23 and thermistor 32 are disposed in the path of air flow fromcondenser 11 to fan 12, resistor 23 is effectively cooled by the airflow and thermistor 32 is made effectively responsive to variations inthe refrigerant liquid-gas interface temperature and the ambienttemperature in providing a temperature-responsive signal to the control30 of the speed control package 22.

Referring now to FIG. 6, control 30 includes a parallel arrangement ofresistor 23, a variable voltage control portion 34, a capacitor and a RFchoke 51 provided for eliminating radio frequency interference. Aminimum voltage for fan motor 13 is provided through resistor 23 andvariable voltage control 34 provides additional voltage to the fan motorto modulate the speed thereof in response to the temperature conditionssensed by thermistor 32 thereby to regulate the operating conditions ofthe refrigerant system. More specifically, the regulation of the fanmotor 13 is a function of the ambient temperature and the load on therefrigeration system represented by the load on the condensing unit. Thecontrol is, therefore, a closed loop control regulating the headpressure of the refrigeration system over the desired range. By makingthe control responsive to the ambient air temperature, control of thehead pressure as a result of the operation of control 34 duringrelatively low ambient temperature conditions provides improvedoperation of the refrigeration system by reducing problems associatedwith liquid return to the compressor. Resultingly, a substantialincrease in the compressor life and reliability is obtained.

Thermistor 32 is spaced rearwardly of the condenser to permit a moredirect response to the ambient air temperature and to provide a moreaccurate sensing of the temperature in the condenser as compared tothose prior art arrangements wherein the temperature sensing device ismounted directly on the condenser coil surface by virtue of avoidingchanges in thermal conductivity due to installation procedures andsubsequent aging of the contacting surface materials.

By way of example only, control 34 includes two pairs of diodes 36, 37,38 and 39, a 16 volt avalanche diode 40, a 2.5 kilohm variable resistor41, a 0.1 kilohm fixed resistor 42, a diode 43, a programmable,unijunction, or PUT, transistor 44, a 0.10 microfarad capacitor 45, a470 kilohm fixed resistor 46, 16 kilohm resistors 47 and 48, 47 ohmresistors 49 and 52, a gated device, herein comprising a conventionalsilicon controlled rectifier, or SCR, 50 and a microhenry RF choke 51.It is to be appreciated that the values of the circuit components can bevaried to suit specific applications or conditions.

The operation of modulating control 34 is extremely simple. Current tothe control is provided between power supply leads L, and L through thefan motor 13. When L, is positive with respect to L current flowsthrough diode 36, SCR 50, diode 38, choke 51 and fan motor 13. Duringthe negative half wave, i.e., when L is positive with respect to Lcurrent flows through fan motor 13, choke 51, diode 39, SCR 50, anddiode 37. Thus, a positive full wave voltage is developed acrossavalanche diode 40. The avalanche diode 40 functions such that voltagethereacross, which is applied to the remaining circuitry, will notexceed the volt breakdown voltage thereof. As the voltage increases fromzero toward a positive value, current flows through resistors 47 and 48which causes the voltage at the junction therebetween, which is coupledto the gate of the PUT transistor 44, to increase. At the same time,current through resistor 46 charges capacitor 45 and after a period oftime determined by the RC time constant of resistor 46 and capacitor 45,the anode of PUT 44 reaches its saturation voltage. PUT 44, in responsethereto, assumes a low impedance state to allow current to flow fromcapacitor 25 through PUT 44 and resistor 49. The junction between PUT 44and resistor 49 is coupled to the gate of SCR 50 and when the voltage atthis gate reaches the breakdown voltage of SCR 50, SCR 50 assumes a lowimpedance state to conduct current in parallel with resistor 23 therebyshunting resistor 23.

As the temperature sensed by thermistor 32 increases, the resistancevalue of thermistor 32 decreases to conduct current through diode 43 tocharge capacitor 45. This reduces the effective RC time constantdetermined by capacitor 45 and, thus, the saturation voltage of PUT 44is reached earlier in the half cycle. The turning on earlier in the halfcycle of PUT 44 causes SCR 50, in turn, to also turn on earlier in thehalf cycle which provides increased shunt current thereby raising thevoltage to the fan motor 13 and causes fan motor 13 to increase inspeed. Variable resistor 41 is provided to vary the conduction angle ofSCR 50. Resistor 42, in series with variable resistor 41, is provided toinsure that this conduction angle can never be decreased below apreselected value. Resistor 52 coupled between diode 36 and avalanchediode 40 isolates the AC voltage applied to the motor from the limitedbreakdown voltage of avalanche diode 40.

Thus, control 34 and thermistor 32 may be built and calibrated as a unitindependently of condensing unit 1 ll effectively eliminating the needfor calibration after assembly to condenser ill or field calibration. Asthe thermistor is spaced from the condenser, electrical insulationproblems are effectively eliminated and the need for maintainedcharacteristics of the surfaces of the condenser and probe iseliminated. The thermistor operation is controlled by variable resistor41 so as to provide a desired set point temperature to maintain the headpressure of the refrigeration system within a desired operating rangenotwithstanding a wide variation in load and ambient temperatureconditions.

Control of the speed of fan motor 13 is substantially instantaneous inresponse to load or ambient tempera ture conditions so as to provide anaccurate closed loop control of the refrigeration system and maintainingthe desired head pressure and back pressure conditions in the system atsubstantially all times.

The thermistor may be caused to have a relatively long time constant byutilization of a relatively large size thermistor to effectivelypreclude instability while yet providing effective following accuratefast response to variations in conditions of the system.

Control 30 is simple and economical of construction while yet providingthe highly desirable features discussed above. By virtue of switchingonly a portion of the voltage by means of control 30 being connected inparallel with fixed resistor 23, radio frequency interference iseffectively reduced and acoustic noise in the fan motor and fan bladesis reduced as a result of the reduction of audio frequency energy.Transient effects on the solid state control 34 are reduced by virtue ofabsorption of energy by resistor 23 thus efiectively reducingvulnerability of control 30 to failure. The power factor relative tocontrol 34 is increased by virtue of the resistor 23 connected in serieswith the fan motor inductance to provide improved operation of thecontrol and speed variations of motor 13 which might be caused bynonsymmetrical firing of the gated control device 50 are effectivelyminimized by resistor 23. Further, failure of control 34 does not causediscontinuation of the operation of fan motor 13 as reduced voltage maycontinue to be supplied to the fan motor 13 by resistor 23. As thewaveform applied to fan motor 13 has low harmonic content and improvedsymmetry, heating of motor 13 is effectively minimized.

The foregoing disclosure of specific embodiments is illustrative of thebroad inventive concepts comprehended by the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

ll. In a refrigeration system for refrigerating a space and having acondenser and motor driven fan for flowing air in heat transferassociation with said condenser and discharging the air outwardly ofsaid space, means for controlling the operation of said fan motorcomprising: resistance means in series with said motor for reducing thevoltage to the motor to reduce the speed thereof, said resistance meansbeing disposed in heat transfer association with the air flowed by saidfan; and control means in parallel with said resistance means forproviding an adjustable additional voltage to said motor for modulatingthe speed thereof, said resistance means having a value preselected topermit operation of the fan motor solely by current flow therethrough.

2. The refrigeration system means of claim 1 wherein said control meansincludes a temperature sensing element disposed adjacent a mid-portionof said condenser for response to temperature conditions in saidcondenser at the level of a liquid-gas interface therein, and means formodulating said additional voltage to the motor to control said level.

3. The refrigeration system means of claim 1 wherein said sensingelement is spaced from said condenser adjacent the liquid-gas interfacetherein.

4. The refrigeration system means of claim 2 wherein said sensingelement comprises a thermistor.

5. The refrigeration system means of claim 2 wherein said sensingelement is disposed in the air flow path downstream of said condenserwhereby said sensing element responds to ambient air temperature as wellas temperature conditions in said condenser.

6. The refrigeration system means of claim ll wherein said control meansis arranged to shunt said resistance means to provide a full speedoperation of said fan.

7. The refrigeration system means of claim 1 wherein said control meansprovides said additional voltage as a variably chopped waveform voltage.

8. The refrigeration system means of claim 1 wherein said control meansincludes means responsive to a temperature condition of said condenserto regulate the condenser head pressure.

9. The refrigeration system means of claim 1 wherein said control meansincludes a thermistor sensing element electrically insulated from thecondenser by said flowed air.

10. In a refrigeration system having a condenser and a fan for flowingcooling air in heat exchange relationship to the condenser, means forflowing refrigerant fluid through the condenser so as to have aliquid-gas interface at a level intermediate the top and bottom of thecondenser, apparatus for controlling the fan comprising: an electricmotor for driving the fan at a variable speed; means spaced adjacent thecondenser for sensing the temperature of the condenser at said liquidgasinterface and the temperature of the ambient air; and means responsiveto said temperature sensing means for varying the speed of said motor toeffectively maintain the level of the liquid-gas interface adjacent thesensing means.

11. The refrigeration system of claim 10 wherein said sensing meanscomprises a thermistor.

12. In a refrigeration system having a fan motor, a temperature sensingmeans, and means responsive to said temperature sensing means forvarying the speed of said motor including a voltage-dropping resistancein series with said motor, control means in parallel with saidresistance for providing additional voltage to said motor comprising: acontrolled conduction device having a gate and connected to said motorfor selectively shunting said voltage-dropping resistance; and gatingmeans to control said controlled conduction means comprising aprogrammable unijunction transistor connected to the gate of thecontrolled conduction device having a R-C timing circuit connected tocontrol said programmable unijunction transistor, said temperaturesensing means being connected to said gating means for 8 sensing meanscomprises a thermistor, said thermistor being connected to said R-Ctiming circuit to modify the time constant thereof in response tovariations in temperature sensed by said thermistor.

1. In a refrigeration system for refrigerating a space and having acondenser and motor driven fan for flowing air in heat transferassociation with said condenser and discharging the air outwardly ofsaid space, means for controlling the operation of said fan motorcomprising: resistance means in series with said motor for reducing thevoltage to the motor to reduce the speed thereof, said resistance meansbeing disposed in heat transfer association with the air flowed by saidfan; and control means in parallel with said resistance means forproviding an adjustable additional voltage to said motor for modulatingthe speed thereof, said resistance means having a value preselected topermit operation of the fan motor solely by current flow therethrough.2. The refrigeration system means of claim 1 wherein said control meansincludes a temperature sensing element disposed adjacent a mid-portionof said condenser for response to temperature conditions in saidcondenser at the level of a liquid-gas interface therein, and means formodulating said additional voltage to the motor to control said level.3. The refrigeration system means of claim 1 wherein said sensingelement is spaced from said condenser adjacent the liquid-gas interfacetherein.
 4. The refrigeration system means of claim 2 wherein saidsensing element comprises a thermistor.
 5. The refrigeration systemmeans of claim 2 wherein said sensing element is disposed in the airflow path downstream of said condenser whereby said sensing elementresponds to ambient air temperature as well as temperature conditions insaid condenser.
 6. The refrigeration system means of claim 1 whereinsaid control means is arranged to shunt said resistance means to providea full speed operation of said fan.
 7. The refrigeration system means ofclaim 1 wherein said control means provides said additional voltage as avariably chopped waveform voltage.
 8. The refrigeration system means ofclaim 1 wherein said control means includes meaNs responsive to atemperature condition of said condenser to regulate the condenser headpressure.
 9. The refrigeration system means of claim 1 wherein saidcontrol means includes a thermistor sensing element electricallyinsulated from the condenser by said flowed air.
 10. In a refrigerationsystem having a condenser and a fan for flowing cooling air in heatexchange relationship to the condenser, means for flowing refrigerantfluid through the condenser so as to have a liquid-gas interface at alevel intermediate the top and bottom of the condenser, apparatus forcontrolling the fan comprising: an electric motor for driving the fan ata variable speed; means spaced adjacent the condenser for sensing thetemperature of the condenser at said liquid-gas interface and thetemperature of the ambient air; and means responsive to said temperaturesensing means for varying the speed of said motor to effectivelymaintain the level of the liquid-gas interface adjacent the sensingmeans.
 11. The refrigeration system of claim 10 wherein said sensingmeans comprises a thermistor.
 12. In a refrigeration system having a fanmotor, a temperature sensing means, and means responsive to saidtemperature sensing means for varying the speed of said motor includinga voltage-dropping resistance in series with said motor, control meansin parallel with said resistance for providing additional voltage tosaid motor comprising: a controlled conduction device having a gate andconnected to said motor for selectively shunting said voltage-droppingresistance; and gating means to control said controlled conduction meanscomprising a programmable unijunction transistor connected to the gateof the controlled conduction device having a R-C timing circuitconnected to control said programmable unijunction transistor, saidtemperature sensing means being connected to said gating means forvarying the operation of said gating means in response to thetemperature sensed.
 13. The refrigeration system of claim 12 whereinsaid controlled conduction device is a silicon controlled rectifier. 14.The refrigeration system of claim 12 wherein said sensing meanscomprises a thermistor, said thermistor being connected to said R-Ctiming circuit to modify the time constant thereof in response tovariations in temperature sensed by said thermistor.